1. Field of the Invention
The present invention relates to improvements in apparatus for controlling the temperature of reactions in biochemical instruments such as, for example, hematology and blood-chemistry analyzers.
2. The Prior Art
In hematology and other blood-analyzing instruments, it is necessary to mix small volumes of a blood sample with specific diluents and/or liquid reagents in order to prepare the samples for subsequent analysis. For example, in hematology instruments, precise volumes of a whole blood sample are sequentially mixed with lysing and stable-lysing reagents in a reaction vessel to achieve a desired homogeneous and diluted concentration of lysed cells that is useful for a subsequent differential white cell analysis; similarly, precise volumes of a whole blood sample, a diluent and a lysing reagent are commonly mixed together to simultaneously dilute the sample and rid the sample of mature red cells in order to prepare the sample for a nucleated red blood cell analysis. In chemical analyzers, it is common to mix small volumes of blood serum with liquid reagents that change color in response to the presence of certain chemical elements or compounds of interest in the sample. In both types of instruments, it is always desirable to carry out the sample-preparation processes at or near an optimal temperature at which the desired results of the chemical reactions and/or the mixing of fluids associated with the sample-preparation processes can be readily achieved. Often, this optimal temperature approximates room temperature, say, about 75 degrees Fahrenheit (° F.). Since regulatory authorities specify that these instruments must be capable of operating satisfactorily within a relatively broad ambient temperature range, e.g., between 60 and 90° F., it is necessary to provide in such instruments some means for controlling the respective temperatures of both the reaction vessels and the samples and reagents in order to assure that sample-preparation is carried out at or near the selected optimal temperature.
In the commonly assigned U.S. Pat. No. 4,858,155 to Okawa et al., apparatus is disclosed for controlling the reaction temperatures in a chemical analyzer. Such apparatus operates to control the temperature of a plurality of reaction vessels or “cells” while simultaneously controlling the temperature of liquids that are fed to each cell without upsetting the temperature of the receiving cell. Such apparatus comprises multiple thermoelectric heating/cooling elements, some serving to individually heat or cool (depending on the ambient temperature) an individual reaction cell to a desired reaction temperature, and others serving to heat or cool individual conduits through which the fluid reagents are supplied to the reaction cells. To control the temperature of the reagents, the reagent conduits are coiled around a cylindrical “slug” of aluminum with which the thermoelectric heating/cooling element is thermally coupled. The coils are sized to hold at least the greatest selectable volume of fluid that is to be delivered to the reaction cells. Thus, upon being heated (or cooled) by the thermoelectric unit, the metal slug transfers (or removes) heat to (or from) the reagent conduits wrapped around it, as well as to the liquid therein. By this arrangement, the temperature of the reagents can be made to conform to a desired temperature before passage to a reaction cell. Meanwhile, control of the reaction cell temperature of a plurality of reaction cells is achieved by thermally coupling an independent thermoelectric heating/cooling element to each of a plurality of thermally-conductive containers to independently control the temperature of each container.
In the apparatus described above, the need for multiple thermoelectric heating/cooling devices to heat or cool the reagent conduits and each of the reagent containers renders the thermal control system relatively complex and costly to manufacture, calibrate and maintain.